AppendixD Part2 AppA

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Appendix ATMs


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TM1: Pretreatment Comparison Investigation


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A TM1-1

TM1: Pretreatment Comparison InvestigationIntroduction

This technical memorandum (TM) summarizes the results from Investigation 1 of the scwd2seawater reverse

osmosis (SWRO) desalination pilot-scale study: a comparison of four different pretreatment system alternatives.

The four systems included slow sand filters (SSF), two different types of hollow-fiber ultrafiltration (UF)

membranes, and granular media filters (GMF). The slow sand filters operated without any chemical addition.

The GMF filters were operated downstream of chemical coagulation, rapid mixing, 3-stage tapered flocculation,

and clarification (rectangular settling basin with plates). The UF systems were operated in several different

modes including without chemical addition, with upstream coagulation and mixing, and with upstream

coagulation, mixing, and settling.

Conclusions

The conclusions from the operational and water quality data are as follows:

Water Quality Goals: All pretreatment systems achieved the target water quality goals with the exception of the TOC

concentration goal of less than 2.0 mg/L. In general, the TOC goal was not achieved by any of the

pretreatment systems when source water TOC exceeded 3.0 mg/L.

The UF membranes produced the lowest levels of turbidity and particle counts. SSF produced the lowest SDI values, and the highest turbidity levels. Conventional treatment produced water with the most variability in SDI results and the highest SDI

and particle counts.

Operational Goals: All pretreatment systems achieved the target operational goals with the exception of the RO system

cleaning interval, which was only achieved by the SSF.

Lower filtration rates, deeper media beds, and smaller media sizes improved the performance ofconventional treatment, while achieving the target operational goals. The tri-media configuration was

able to reduce, but not eliminate iron breakthrough with conventional treatment using an iron-basedcoagulant.

The slow sand filter achieved the water quality and operational goals without coagulant chemicaladdition.


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City of Santa Cruz & Soquel Creek Water District TM1: Pretreatment Comparison Investigation

TM1-2 A

The Zenon submerged UF system also achieved the water quality and operational goals withoutcoagulant chemical addition except the RO system cleaning interval goal. However, coagulant

addition prior to UF filtration provided increased removal of dissolved organics, reduced fouling rates

of the UF membranes (sustaining lower differential pressures), and appeared to reduce RO fouling

during the red tide simulation event.

The Norit UF achieved the water quality and operational goals except the RO system cleaning intervalgoal. Coagulant addition was required to achieve the target operational goals even at reduced flux and

recovery rates.

Higher levels of polysaccharides and algal cell breakage were observed with higher levels of differentialpressure across the UF filters, especially when coagulant was not added.

All filtrations systems removed turbidity, suspended solids, and particles to levels that indicate thatalgal cells will be removed readily by each of the four pretreatment filters. However, the data suggests

that dissolved organics released by algae contribute to RO fouling and that algal cell breakage (a.k.a.,

lyse) correlated with high differential pressures during pretreatment system filtration and

backwashing. Related observations are as follows:

Coagulation, flocculation, and clarification upstream of UF or GMF filtration decreased foulingduring algal blooms. Futhermore, it is anticipated that utilizing a clarification system that enhances

algae removal prior to GMF or UF filtration may further reduce RO fouling. One option is dissolved

air flotation which uses air to float the floc and buoyant material (e.g., algae) out of the water

stream instead of using gravity to settle out the material. Although this process was not tested at

the pilot facility, it is anticipated to improve algae removal based on industry experience1 and

recommendations from Dr. Raphael Kudela, a marine algae researcher at UC Santa Cruz.

SSF utilizes a low filtration rate and differential pressure which is expected to reduce algal cellbreakage during filtration. Furthermore, the biological activity in the filter is expected tometabolize some of the dissolved organics released by algae. This is one hypothesis why fouling

was not observed downstream of the SSF during algal blooms.

Cartridge Filter:The cartridge filters were replaced more frequently on average downstream of the SSF and GMF than

downstream of the UF systems. The differential pressure increase across the cartridge filters downstream of the

UF systems averaged approximately 1 psi per month over the 13-months of testing, which indicates infrequent

cartridge replacement. The differential pressure buildup downstream of the GMF systems averaged

approximately 2 to 3 psi per month during optimized coagulation, filtration, and backwashing and

approximately 5 psi per month when iron breakthrough was observed. The differential pressure buildup

downstream of the SSF systems averaged approximately 2 to 4 psi per month over the 13-months of testing.

1 Dissolved Air Flotation and Me. Dr. James Ezwald. Water Research, Article in Press, 2010. Retrieved at

http://dx.doi.org/10.1016/j.watres.2009.12.040


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TM1: Pretreatment Comparison Investigation City of Santa Cruz & Soquel Creek Water District

A TM1-3

RO Fouling: The RO system downstream of conventional treatment had the most frequent cleaning interval. This

was primarily due to iron-particulate fouling caused by particle and iron breakthrough through the

GMF filters after iron-based coagulant addition. Moderate levels of fouling were also observed during

dense algal blooms.

The RO system downstream of the SSF did not require cleaning during the study, had the lowestamount of flux decline and had the lowest amount of foulant observed on the membrane surface.

The RO systems downstream of the UF systems had moderate levels of biofouling during dense algalblooms. The most rapid flux decline was observed when a coagulant was not being added prior to

filtration and differential pressures typically exceeded 6 psi (and at times increased to levels greater

than 10 psi) during the fall prorocentrum bloom event. It is speculated that the high differential

pressures increased shear and algal cell breakage within the pretreatment system, which led to higher

rates of RO fouling.

Additional Observations

Additional observations from the pilot program and from the desalination industry are as follows:

Adding a pre-oxidant, increasing media depth, and decreasing media size will improve the waterquality of conventional treatment for a full-scale plant. A well-operated and well-designed

conventional pretreatment system is adequate for municipal-scale desalination plants. Note that the

planned pretreatment system for the proposed 50 mgd SWRO plant in Carlsbad, CA was switched from

UF to conventional treatment with low-rate, deep bed, tri-media, gravity filters because of similar

concerns over algal cell breakage and to reduce costs.

UF systems provide more reliable filtered water quality when compared to conventional treatmentduring changes in source water quality and plant operations, and will reduce O&M optimization to

prevent fouling. UF membranes also provide the greatest amount of microbial removal credits fromDPH. The disadvantage of UF systems is the potential to rupture algal cells during filtration and

backwashing, which may be mitigated by improving algae removal prior to filtration.

Slow sand filters had excellent water quality and operational performance during this pilot test, mimicthe biological process of beach wells, require no chemicals or pumping power, but require more land

than either conventional pretreatment or UF pretreatment.

RO membrane fouling, cleaning and replacement are unavoidable with any pretreatment system, sothe pretreatment decision is ultimately based on a balance of costs and reliability of water production.

Project specific design criteria, site plans and capital and costs for the pretreatment alternatives will be

presented in Technical Memorandum No. 12.


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TM1-4 A

Background

The reverse osmosis (RO) process requires little maintenance and downtime when the source water is very

clean. However, RO desalination plants with ineffective pretreatment require frequent cleanings and

membrane replacement, resulting in excessive downtime and operation and maintenance costs2.

Open intake seawater desalination plants have been operated around the world for decades utilizing chemical

coagulation, clarification and granular media filtration as pretreatment. However, many plants experience

fouling: biological, organic, particulate or scaling, which requires shutdowns and cleanings every 1 to 6 months

and RO membrane replacement every 3 to 6 years. Some plants in the Persian Gulf shut down during red tide

events due to increased rates of fouling3,4. Biological fouling is of particular concern as it increases the power

required for desalination and is often difficult to remove without harsh cleaning solutions5 that increase

membrane replacement frequency to achieve water quality objectives6.

More recently, desalination plants are being constructed with membrane pretreatment systems such as

microfiltration and ultrafiltration (UF). The pretreatment systems typically reduce colloidal and particulate

fouling; however, biological fouling is encountered at some installations7.

The purpose of Investigation 1 was to test four different pretreatment filters side-by-side to determine the

optimum pretreatment system for the source water in Santa Cruz to minimize fouling.

Pilot-scale Equipment Description

The process schematic is presented in Figure 1. A brief description and design criteria tables are presented in

Appendix B for the equipment used during the pilot test program following the data charts presented in

Appendix A.

The pretreatment systems that were tested during the program are as follows:

1. Conventional treatment: defined as chemical coagulation, rapid mixing, 3-stage tapered flocculation,and clarification (rectangular settling basin with plates) followed by pressure granular media filters

(GMF). After initial testing of filtration rates between 3 to 6 gpm/sf, it was determined that the GMF

would be operated at a conservative loading rate of 3 gallons per minute per square foot (gpm/sf) as

pressurized, constant rate filters because this rate provided the best results in terms of SDI. Backwashes

were performed with air and water to clean the media. The following three GMF media configurations

were evaluated:

2 Reverse Osmosis and Nanofiltration. AWWA Manual M46. Second Edition. American Water Works Association, 2007.3 'Red tide' forces desalination plant closure. Andy SambidgeArabian Business.com.. November 2008; Retrieved at

http://www.arabianbusiness.com/538468-red-tide-forces-desalination-plant-closure.4 Tech focus: Dissolved air flotation technology. Peter WardArabian Oil and Gas.com.. May 2009; Retrieved at

http://www.arabianoilandgas.com/article-5488-tech-focus-dissolved-air-flotation-technology/5 Cleaning solutions with high pH levels are typically required to remove biofouling; however, the high pH levels are also

damaging to the membrane surface and may decrease the effective salt rejection of the membranes.6 Seawater Desalination Membrane Biofouling Project Scoping Meeting. Information presented by Nikolay Voutchkov at

the University of California, Irvine December 4 th, 2008.7 Reversible and Irreversible SWRO Membrane Fouling Owing to Algae Blooming. Dr. Ahmed Hashim and Professor Kenneth

Persson. International Desalination Association World Congress. October 2007.


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Flocculation/

Sedimentation

Slow Sand Filter No. 1

Ocean

Intake

Strainer

* RO Permeate and RO Concentrate are mixed in the blending tank and then discharged to the LML Seawater system

HoldingTank

Rapid

Mix

Granular Media

Filter No. 1

Granular Media

Filter No. 2

Optional Feed Line when

Operating without a Coagulant

Optional Feed Line when

Operating without a Coagulant

or without Sedimentation

Optional Feed Line

when Operating

without Sedimentation

Holding

Tank

RO Feed

Tank

Cart

Filt

Cart

Filt

CartFilt

RO Feed

Tank

Flocculation/

Sedimentation

RapidMix

Pressurized UF

Submerged UF

HoldingTank

RO FeedTank

RO Feed

Tank

Cart

Fil

Slow Sand Filter No. 2

W:\REPORTS \Santa Cruz City of\Desal Pilot_Final Report_09\Graphics\Fig1_Basic Pilot Plant Flow Schematic.ai 06/10/09 J J T


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A TM1-5

Mono-medium (40 inches of 1.0 millimeter [mm] anthracite) with an approximate L/d ratio of1,000,

Dual-media (20 inches of 1.0 mm anthracite over 10 inches of 0.5 mm sand) with an approximateL/d ratio of 1,000 and

Tri-media (20 inches of 1.0 mm anthracite over 8 inches of 0.5 mm sand over 6 inches of 0.25 mmgarnet) with an approximate L/d ratio of 1,500.

2. Slow sand filtration (SSF): defined as very low rate filtration (0.1 to 0.2 gpm/sf), deep bed sand filterswith no chemical addition, clarification or backwashing. The filter beds were cleaned by harrowing,

which consisted of scouring the top of the media bed with a rake and discharging the water column to

waste. The following two media configurations were evaluated (note: the sand layers were measured

at 30 inches during installation and 24 inches at the end of testing due to compaction and sand

removal during cleaning):

SSF1 (24 inches of 0.35 mm sand over 10 inches of gravel), and SSF2 (24 inches of 0.80 mm sand over 10 inches of gravel).

3 & 4. Ultrafiltration (UF) Membrane Filtration: hollow-fiber membranes with pore sizes of 0.04 micron or less

(Zenon UF submerged membranes with nominal pore size 0.04 micron and Norit UF pressurized

membranes with nominal pore size 0.01 micron). The UF membranes were operated in a dead end

filtration mode with and without coagulant chemical and clarification. The UF membranes were cleaned

with a combination of the following:

1-minute backwashes every 40 to 60 minutes (air and water for the Zenon UF and water only forthe Norit UF).

15-minute chemically enhanced backwashes (CEB) multiple times per week (sodium hypochloriteand citric acid for both the Zenon UF and Norit UF).

4- to 8-hour intensive cleanings known as clean-in-place (CIP) multiple times per year (sodiumhypochlorite and citric acid were used for both the Zenon UF and Norit UF).

Pilot Plant Test Period

Testing at the pilot plant occurred over a period from March 20,, 2008 to April 15, 2009.

Source Water Quality

The ocean off the coast of Santa Cruz can be characterized as having three distinct water quality conditions:

typical, algal bloom events, and winter storm events, which are described for the purpose of this memorandumas follows:

During typical water conditions, the turbidity and total organic carbon (TOC) concentrations arerelatively low (turbidity less than 5 Nephelometric Turbidity Units (NTU) and TOC less than 1.3

milligrams per liter [mg/L]).


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TM1-6 A

Algal bloom events occur year-round; however, large algal blooms such as red-tide events occurbetween the months of September through December. Large algal bloom events are marked by high

algae counts, moderate turbidity values, and TOC concentrations that can exceed 15 mg/L. A red tide

event was artificially created on April 13th and 15th by spiking concentrated algal cells to a level of 30

micrograms per liter (g/L) of chlorophyll; the event is referred to as the red tide simulation in this

memorandum.

Storm events typically occur between December and March. Rainfall and runoff from local streams andcreeks combine with wintertime ocean currents and upwelling to significantly increase the turbidity to

levels that may exceed 50 NTU. The data presented herein was collected during the most significant

storm event which occurred during the week of February 16th.

Source water quality conditions during the 12 months of pilot testing are summarized in Table 1.

Table 1. Observed Source Water Quality Data Summary

Observed Water Quality

Periods & Events

Spring and

Summer

Fall & Winter

(Non-storm

conditions)

Fall Algal

Bloom

Winter Storm

Event

Spring Algal

Bloom

Red tide

simulation

Event

Water Quality

ParameterUnits

April August

2008

September2008 March

2009

November

2008

February 16,

2009

Late March

Early April 09

Mid-April

2009

pH

(mean)pH Units 8.0 8.0 8.0 7.9 7.9 7.9

Temperature

(range)oC 12.0-18.1 9.5-15.8 13.4-15.6 12.8-14.1 11.9-14.2 11.1-13.4

Turbidity

(range)NTU 1.5-4.2 2.0-3.5 1.1-2.0 8-40 1.8-2.8 8-15

Particles

(> 2 m)

(mean)

No. per

100 mL10,530 9,860 12,340 14,110 9,690 12,790

TOC

(range) mg/L 1.0-1.2 1.1-6.0 3.2 2.5 3.4-13.0 7.2

DOC

(range)mg/L 0.9-1.1 1.3-3.8 2.9 2.0 3.1-12.0 4.3

Chlorophyll

(typical)g/L

2.3-21.2

(at SC

Wharf)

1.0 2.7 0.7 9.2 30

Algal Cell Count

(typical)

Cells per

Liter

Not

counted15,000 28,000


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A TM1-7

chemical consumption, washwater and sludge production, performance of the RO system with respect to

fouling control, and life-cycle costs.

The pretreatment water quality goals are presented in Table 2.

Table 2. Summary of Pretreatment Goals

Water Quality and

Operational GoalsConventional Treatment Slow Sand Filtration

UF Membrane

Pretreatment

SDI(1)

(SDI15 Units)

4.0(2) (99% of the time)

3.0 (90% of the time)

TOC

(mg/L) 2.0(2)

Turbidity

(NTU) 0.1(2)

Removal of Particles

>2 microns 99.0% 99.0% 99.99%

Filter Run Time 24 hours 3 at gpm/sf 2 weeks at 0.1

gpm/sf

> 40 minutes at

25 gfd for Zenon UF

50 gfd for Norit UF

Chemically Enhanced

Backwash Intervaln/a n/a 24 hours

UF Membrane Clean in

Place Intervaln/a n/a 2 months

RO Membrane Clean in

Place Interval(3) 5 months 5 months 5 months

(1) SDI calculated for 500 mL of sample at fifteen minutes.(2)Typical pretreatment goals listed by RO membrane manufacturers for open intake seawater desalination.(3)The interval assumes that a cleaning is required when an increase in normalized differential pressure is greater than 15% and/or

a decrease in normalized specific flux or permeate flow of greater than 10% is observed based on Hydranautics Technical Service

Bulletin 107 retrieved at http://membranes.com/docs/tsb/tsb107.pdf.

Pretreatment Testing Results

Table 3 presents a summary of the pretreatment water quality and operational results from the testing. Note

that all water quality and operational goals were achieved except the following:

TOC concentration goal - the four pretreatment systems were able to achieve the TOC concentrationgoal when source water concentrations were less than 3.0 mg/L as expected. No pretreatment system

was able to achieve the goal when the source water concentration was greater than 3.0 mg/L. Thus,

TOC removal percentage will be used in addition to TOC concentration to compare the pretreatment

systems.

RO membrane cleaning interval goal downstream of conventional treatment - The goal was notachieved downstream of GMF pretreatment due to observed fouling during algal blooms and

increases in differential pressure caused by iron breakthrough. The goal was not achieved downstream

of UF pretreatment due to observed fouling during algal blooms.


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TM1-8 A

Table 3. Pretreatment Results Summary

Water Quality and

Operational GoalsConventional Treatment Slow Sand Filtration UF Membrane Pretreatment(1)

SDI

(SDI15 Units)

4.0(99% of the time) 3.0(90% of the time)

3.0(99% of the time)

3.0

(99% of the time)

TOC Removal % and

Concentration (mg/L)

11-55%

0.7-5.1 mg/L

5-42%0.7-5.7 mg/L

7-35%with coagulant0-4% without coagulant

0.8-5.2 mg/L

Turbidity

(NTU) 0.10 0.15 0.03

Removal of Particles

>2 microns 99.1% 99.3% 99.99%

Filter Run Time 24 hours at

3 gpm/sf

2 weeks at

0.10 gpm/sf for SSF1

0.15 gpm/sf for SSF2

40 minutes at

30 gfd for Zenon UF

55 gfd for Norit UF

Filter Washwater

Requirements Based on

Filter Run Time

2-4% of total flow

or 0.1-0.3 mgd at

max flow (6.1 mgd)

0.4-0.6% of total flow or

0.02-0.04 mgd at max

flow (6.1 mgd)

5-8% of total flow

or 0.3-0.5 mgd at

max flow (6.1 mgd)

Chemically Enhanced

Backwash Intervaln/a n/a 24-48 hours

UF Membrane Clean in

Place Intervaln/a n/a

2-3 months for Zenon UF

3-6 months for Norit UF

RO Membrane Clean in

Place Interval(2)

Run 1: > 4 months with dual-

media filter

Run 2: 1-2 months with dual-

media filter and >2 months

with tri-media filter

Run 1: > 5 months

Run 2: > 5 months

Run 1: > 5 months

Run 2: 3 months; fouling only

observed during algal blooms

(1) The Zenon UF membrane was able to achieve all pretreated water quality goals except the TOC concentration of less than 2.0

mg/L with and without coagulant addition.(2) RO system Run 1 occurred between March and September 2008. Run 2 began in September, after all RO membranes were

replaced with identical Toray 810L SWRO membranes, and ended in April 2009.

RO Membrane Fouling ResultsDuring of the first portion of RO membrane Run 1 between March and July 2008, the RO membranes were set

at a conservative operating flux rate of 8 gallons per foot per day (gfd). During this time significant fouling was

not observed, so the flux was increased to a less conservative value of 10 gfd between July and September. In

September, the RO membranes from Run 1 were replaced with new RO membranes to begin Run 2.

The flux remained at 10 gfd and noticeable fouling was observed during the following three distinct periods

during Run 2:

Fouling was observed downstream of conventional treatment and both the Zenon and Norit UFmembranes during the fall algal bloom in mid-December. The fouling was observed as reductions in

specific flux. The fouling downstream of conventional pretreatment occurred even though coagulation

and sedimentation were producing settled water turbidity levels of less than 1 NTU and the GMF filters

were achieving SDI and turbidity goals. The fouling downstream of the UF systems observed at this


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A TM1-9

time occurred during a period when the UF systems were treating raw seawater (i.e., when no

coagulant or flocculation was utilized upstream) and were achieving SDI and turbidity goals. The

fouling was most prevalent downstream of the Norit UF, which could not sustain low differential

pressure levels without a coagulant chemical. The high differential pressure levels may have increased

algal cell breakage which is a source of high molecular weight dissolved organics (e.g.,

polysaccharides) which are believed to be the primary sources of membrane biofouling. The nature of

the fouling is summarized below in Table 4. The fouling was considered to be biofouling as a pH of

approximately 12 was required to recover the specific flux of the SWRO membranes.

Iron-based particulate fouling was observed downstream of conventional treatment between October2008 and March 2009. The fouling was observed as increased differential pressure across the RO

membranes. The differential pressure was easily recovered with a low pH clean using citric acid. The

nature of the fouling is summarized below in Table 4. Iron carryover was observed downstream of the

conventional treatment prior to this period, but it resulted primarily in increased rates of fouling across

the cartridge filters prior to the RO membranes.

Fouling was observed downstream of conventional treatment and Zenon UF systems during the redtide simulation event. The fouling was observed as reductions in specific flux in the RO membranes.

The fouling downstream of the Zenon UF system correlated with a period when the system was

treating raw seawater (i.e., when no coagulant or flocculation was utilized upstream).

Figures A-4 through A-7 in Appendix A present the RO fouling trends (differential pressure and specific flux) for

the RO membranes downstream of each of the pretreatment systems.

The results from the RO membrane autopsy are presented below in Table 4; the autopsies were performed in

January after the most significant reductions in specific flux were observed, but prior to membrane cleaning.

Noticeable fouling of the RO membranes downstream of the slow sand filters did not occur. A small amount of

inorganic material was identified on the membrane surface from the autopsy results; however, this did not

seem to detract from performance of the RO membranes downstream of the SSF.


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TM1-10 A

Table 4. RO Membrane Autopsy Results Following the Fall Algal Bloom

RO Pretreatment

Description

RO Downstream of Zenon

Membrane

RO Downstream of Norit

Membrane

RO Downstream of

Slow Sand

RO Downstream of

Conventional Treatment

Membrane Surface

Scrapings

Disassembled

Membrane

Description of theFouling Layer on

the Membrane

Surface

Thin layer of organiccolloidal material with

some slime and iron

Dark biofouling layerwith slime, colloids

and some iron

Inorganic layercomposed mostly of

silica with some

aluminum and iron

Thick iron-based layerintermixed with

biofouling layer

Decrease in

Normalized

Specific Flux

7% >10% 2% 7%

Increase in

Normalized

Differential

Pressure

4% 7% 3% >10%

Cleaning Results

Low pH recovered


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A TM1-11

Impact of Storm & Algal Bloom ConditionsSDISDI values were monitored daily in the filtered water streams to assess the RO membrane clogging potential

of the pretreated water. It should be noted that SDI values typically increased more from small colloidal

material and dissolved organics in the filtered water than from larger particles such as sand. The SDI results are

summarized in Figure 2.

The SDI results produced by both the Norit and Zenon UF membranes were typically less than 2.3 including

during the most significant storm event, but increased to an average of 2.9 during the red tide simulation

event. The SDI values produced by both SSFs were typically less than 2.2 during typical conditions, but

increased during the red tide simulation event and storm events. The SDI values produced by conventional

treatment typically achieved a value at or less than 3.0 during typical conditions, but increased during the red

tide simulation event and storm events. It is speculated that the UF systems were impacted less by the stormevent as the UF filters were able to better remove the small colloidal material that became suspended within

the water column during the storm.

Figure 2Summary of Pretreatment SDI Results forDifferent Source Water Quality Conditions


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TM1-12 A

TurbidityTurbidity results were assumed to be a surrogate for removal of very small suspended solids such as fine silts

and other material that adsorbs light. Removal of turbidity is necessary to reduce particulate and colloidal

fouling of the cartridge filters and RO membranes in the desalination system. Figure 3 presents the turbidity

performance of the pretreatment trains during different source water quality conditions.

The filtered water turbidity results for the pretreatment systems can be summarized as follows:

The UF filtered water turbidity was typically less than 0.03 NTU and was not significantly impacted bychanges in source water turbidity, flux rates or coagulation modes. There was a slight increase

observed during the algal spiking event; however, the turbidity was still below 0.07 NTU.

The filtered water turbidity of the SSF trains varied typically between 0.08 and 0.13 NTU (the resultsfrom SSF2 were typically 0.01 to 0.03 higher than SSF1). Filtered water turbidity tended to follow the

source water turbidity trends and would occasionally increase 5 to 20% temporarily (less than 8 hours)

after harrowing. The turbidity also increased during the algal spiking and storm events.

The filtered water turbidity produced by conventional treatment typically ranged from 0.06 to 0.10NTU. The filtered water was directed to waste until the turbidity was less than 0.10 NTU and the filters

Figure 3Summary of Pretreatment Turbidity Results forDifferent Source Water Quality Conditions


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A TM1-13

were typically backwashed prior to the turbidity level increasing above 0.10 NTU. It was also observed

that parameters including coagulant dose, floc size, filtration rate, and backwash interval had to be

optimized and carefully adjusted to achieve the target pretreatment goals including turbidity. There

was a slight increase during the major storm event in February; however, the filters continued to

achieve the goal of


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TM1-14 A

The pictures of the RO membrane and fouling layer included in Table 4 are one example of the observed iron

breakthrough and fouling; however, the iron breakthrough was evaluated on a daily basis by observing the

color on the SDI paper filters and observed as fouling across the cartridge filters.

Figures 5 and 6 display pictures of the iron observed on the SDI filter papers and a cartridge filter downstream

of conventional treatment compared to UF and SSF pretreatment.

Figure 4Summary of Pretreatment Particle Removal Results forDifferent Source Water Quality Conditions


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A TM1-15

Figure 6Pictures of New and Used 5-micron Cartridge Filters; (from left to right): filter downstream ofconventional treatment, new cartridge filter, filter downstream of slow sand filter, filterdownstream of UF membranes.

Figure 5SDI filter papers (from left to right): SSF1, Norit UF, SSF2, GMF2, and Zenon UF on August19,2008 and SSF1, Norit UF, SSF2, GMF2, and Zenon UF on December 19, 2008 Note ironbreakthrough on GMF 2. Note GMF 1 was offline on both of these days


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TM1-16 A

A common method to improve the removal of iron by pretreatment filters is to add an oxidant10 such as

chlorine or chlorine dioxide upstream of the filters. A low dose of chlorine dioxide was added upstream of the

flocculation and sedimentation process during ferric chloride addition to assess the improved iron removal

through the pretreatment systems. The target dose was 0.5 mg/L; the observed ORP level was 550 millivolts

(mV), which was almost double the ambient level of 300 mV. Table 5 summarizes the reduction in iron in the

pretreated water before and after oxidant addition.

Table 5. Summary of Iron Concentrations in the Pretreated Water Streams Before and After Oxidant

Addition

Treatment

DescriptionConventional Treatment Slow Sand Filtration UF Membrane Pretreatment

Iron Concentration

Before ClO2 Addition

(g/L)

17.0 10.0 8.9-14.0Iron Concentration After

ClO2 Addition

(g/L)


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A TM1-17

Filtered water samples were collected from each of the pretreatment systems to assess the removal of

polysaccharides. Suites of typical carbohydrates (fucose, rhamose, arabinose, galactose, glucose, mannose, and

xylose) and amino acids (14 acids including glycine, aspartic acid, alanine and glutamic acid) which make up

the majority of polysaccharides found in the open ocean were analyzed by researchers at Stonybrook

University and the University of South Carolina. Polysaccharides are typically found in the dissolved form andpass through pretreatment filters. Studies performed at existing full-scale seawater desalination facilities in

Europe showed that coagulant chemicals and the slow rate biological filtration by beach wells often aid in the

removal of polysaccharides.11 These results presented in Figures 8 and 9 were confirmed in our testing as the

removal of polysaccharides by the UF systems improved with coagulant addition and as the removal was

relatively high through the SSF, which utilized slow-rate biological filtration without coagulant addition. Note

that the sample collected in January of 2009 for carbohydrates was omitted from the chart because the

samples thawed during shipping, which nullified the data.

11Chemical Characterization of Membrane Foulant Recovered from RO Desalination and NF Treatment Trains. J.P. Cruoe, L.

Monamert, and J. Labanowski. Presented at the AWWA Membrane Technology Conference in Memphis, Tennessee.

March, 2009.

Figure 7Summary of Pretreatment TOC Removal Results forDifferent Source Water Quality Conditions


21/254


TM1-18 A

Figure 8Summary of Amino Acid Concentrations for Three Different Sampling Events

Figure 9Summary of Carbohydrate Concentrations for Two Different Sampling Events


22/254


A TM1-19

As noted above, the background concentration of DOC in the open ocean is approximately 1.0 mg/L. Higher

observed concentrations often correlate with another source such as surface runoff or algal bloom events.

Dissolved organics including polysaccharides are secreted from algal cells during normal activity, but higher

DOC concentrations are observed when these cells break.

Recent research

4

suggests RO biofouling occurs more rapidly when this DOC is released within thepretreatment process. Data collected at the desalination pilot plant in Carlsbad, California, provides a

correlation between the differential pressure of a pretreatment system, increased levels of algal cell breakage,

and increased levels of biofouling4. Similar results were demonstrated with artificial laboratory tests that used

UF membranes upstream of RO; the results indicated that an increased amount of organic matter was able to

pass through the pretreatment filter during increased levels of algal breakage through shear.12

Testing was performed at the pilot plant in Santa Cruz to test this theory of algal cell breakage within

pretreatment systems. It was recommended that DOC to total nitrogen ratios be calculated before and after

filtration to assess whether algal cells are breaking. If the DOC concentration increases after filtration, but the

DOC:N ratio doesnt change, then the increase can be attributed to filter integrity issues or new growth. If the

DOC concentration increases and the DOC:N ratio increases, the increase can be interpreted as cell breakage.

Figure 10 presents the DOC to total nitrogen ratios during the red tide simulation event. Note that the levels of

differential pressure (DP) for each pretreatment system are included in the graph.

Higher differential pressures correlated with increases in both DOC concentrations and DOC:N ratios indicating

that algal cells were breaking during filtration. There was some improvement with coagulant addition and

clarification; however, it was mostly dependant on differential pressure.

The implications of this are that removing the majority of algal cells prior to filtration will likely decrease

biofouling when using pressurized filters. Coagulation and clarification aids this process; however, using

dissolved air flotation (DAF) improves removal of algal cells13 as it uses air to remove buoyant material in lieu of

conventional sedimentation basins which rely on settling by gravity for clarification. Another implication is that

gravity granular media filters would be preferred over pressurized filters if conventional treatment is the

selected pretreatment process.

12 Effects of Shear on MF and UF Fouling by Bloom-Forming Algae in a Seawater Desalination Treatment Train. D.A. Ladner, D.R.

Vardon, and M. M. Clark. Presented at the AWWA Membrane Technology Conference in Memphis, Tennessee. March,

2009.13Principles and applications of dissolved air flotation. Dr. James Ezwald. Water Science and Technology Volume 31, Issues 3-

4, 1995.


23/254

Appendix AData Charts


24/254

Source Water QualityData Charts


25/254

FigureA

1.

SourceWaterTurbidityData

Raw

Wa

ter

Be

fore

Stra

iner

(Da

ilygra

b)

Raw

Wa

tera

fter

Stra

iner

40

HighTurb

idity

Even

ts

Imme

diatelyfollow

ingL

ML

Intakean

dPump

Repair

30

25

StormEvent

20

urbidity(NTU)

15

RedTide

Simulatio

nEvent

510 0 3

/26

4/15

5/5

5/25

6/14

7/4

7/24

8/13

9/2

9/

22

10

/12

11

/1

11

/21

12

/11

12

/31

1/20

2/9

3/1

3/2

1

4/10

Date


26/254

19,0

00

20,0

00

21,0

00

22,0

00

23,0

00

24,0

00

25,0

00

>2microns)per100mL

FigureA

2.

Source

Water

ParticleCountD

ata

SourceWaterPartic

leCountsatthePilotPlant

10,0

00

11,0

00

12,0

00

13,0

00

14,0

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15,0

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16,0

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17,0

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18,0

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3/26

4/16

5/7

5/28

6/18

7/9

7/30

8/20

9/10

10/1

10/22

11/12

12/

3

12/24

1/14

2/4

2/25

3/18

4/8

ParticleCounts(

Date


27/254

gureA

3.

SourceWaterChlorop

hyll,

TotalOrganicCarbon,

Chlorophyll(atpilotplantintake)

Chlorophyll(atSCWharf)

TotalOrganicCarbon

600,0

00

an

gae

e

ount

ata

Cells

perliter(atpilotplantintake)

Redtide

simulation

500,0

00

Chaetocero

s

bloom

event

400,0

00

ter

300,0

00

lgalCellsperLi

Chaetoceros,Laurdia,

&Skeletomabloom

Cha

etoceros&

Protoperidinium

bloom

Akashiwosanguine

a

bloom(redtidespecies)

200,0

00

C

haetoceros

b

loom

Prorocentrumbloom

(redtidespecies)

Ceratium

bloom

Cha

etoceros&

ske

letomabloom

100,0

00

0

D


28/254

RO Fouling TrendData Charts


29/254

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30/254

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32/254

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33/254

Appendix BPilot Plant Equipment

Description and Design Criteria


34/254

Appendix BPilot Testing Equipment

A B-1

Pilot-scale Equipment DescriptionThe equipment for the pilot test program was custom-fabricated and/or procured

from experienced manufacturers to evaluate scale-up of alternative pretreatment and

RO process configurations and to provide flexibility to operate over a range of

operating values for treatment optimization. The equipment was located inside a

2,400 square foot building constructed specifically for the testing program.

A schematic of the treatment process is presented in Figure 1 in the TM. Design

criteria tables are included following this page.

See Technical Memoranda No. 2 for a description of the reverse osmosis (RO)

desalination systems.

Raw Water Storage and Supply

Key equipment for raw water storage and supply included a 100 micron rotating disc

strainer, two 2,250 gallon storage tanks, a raw water pump, and ancillaryinstrumentation for monitoring raw water quality.

Pretreatment Equipment

Key equipment included two coagulation, flocculation, and sedimentation basins, two

24-inch diameter pressure granular media filters, two 8-ft. diameter slow sand filters,

two UF membrane systems, chemical feed systems, ancillary storage tanks, ancillary

pumps, and ancillary instrumentation.

Coagulation was accomplished by feeding ferric chloride into a static mixer followed

by flocculation which occurred in a 3-stage basin with vertical shaft mixers and a

detention time of 30 minutes. Sedimentation, when utilized, occurred afterflocculation in a rectangular basin equipped with plate settlers.

Granular media pressure filter 1 (GMF1) originally contained 40-inches of a coarse

anthracite mono-media, but was replaced near the end of the study with tri-media

including anthracite, sand and garnet. GMF2 contained 30-inches of anthracite/sand

dual-media. Each operated at a filtration rate of 3 gpm/sf. Slow sand filter 1 (SSF1)

contained 24-inches of fine sand media and SSF2 contained 24-inches of coarse sand

media. Each was operated at a filtration rate of 0.08 to 0.15 gpm/sf.

UF membrane equipment was procured from Norit and Zenon to evaluate a range of

flux rates and to investigate different backwash and chemical clean procedures. TheNorit pressure unit utilized Norit XIGA UF membranes and the Zenon unit utilized

Zeeweed 1000 immersed (submerged) UF membranes. Key equipment for membrane

pretreatment included the UF filtrations skids, an air compressor, ancillary storage

tanks and ancillary pumps. Instrumentation, chemical feed systems, pumps and other

equipment necessary for UF operation and treatment are provided by the membrane

vendors and mounted on each skid.


35/254


A B-2

Table B-1

Raw Water Storage and Supply Design Criteria

Item Quantity Unit Description/Notes

Raw Seawater Storage Tank 2 No. HDLPE; two tanks in series due to limited space.

Capacity at 50 gpmVolume (each) 2,250 gallonsStorage capacity 90 MinutesDimensions Each tank

Diameter 8 feetHeight 9.5 feet

Raw Seawater Pump 1 No. FRP /PVC wetted parts.Flow 30-50 gpm Flow split to pretreatment processes.Head 50 FeetPower 230/460 Volt

Strainer 1 No. Self-backwashing. All plastic wetted parts.Size 100 micronCapacity 50 gpmMinimum Backwash Flow 40 gpmMinimum Backwash Pressure 30 psi

Maximum Operating Pressure 140 psiBackwash Diff. Pressure 3-10 psi Adjustable

Table B-2Rapid Mix, Flocculation, and Sedimentation (Clarification) Basin Equipment Design Criteria


Flash Mix 2 No. Static mixer (PVC)Flowrate 25 gpm Each mixerDiameter 1 inchMinimum Velocity Gradient 1,000 sec

-

Chemical Injection Ports 3 No. Upstream of mixerFlocculators 2 each 3 stage, horizontal flow w/ vertical shaft impellers

Flow 25 gpm Each flocculator

Hydraulic Detention Time 30 minutes 10 minutes each stageStages/basins 3 No.

Length 3 ft. Each stageWidth 3 ft. Each stageHeight 4 ft. Each stage

Mixing EnergyStage 1 40-80 sec

-Mean velocity gradient

Stage 2 40-60 sec-

Mean velocity gradientStage 3 10-40 sec

-Mean velocity gradient

Sedimentation Tank (with Plate Settlers) 2 No. Single stage; horizontal flow w/ plate settlersFlow 25 gpm Each sedimentation basinHydraulic Detention Time 21 minutes At 25 gpmBasin 1 No.

Length 6 ft.Width 3 ft.

Height 5 ft.Surface Loading 0.52 gpm/ft With all plates inserted @ 25 gpmSludge Conveyance

Chain & Flight TimedProgressing Cavity Pump 5 gpm


36/254


A B-3

Table B-3

Granular Media Filter Equipment Design Criteria

Item Quantity Unit Description/NotesMedia Filter 2 each Capable of operating in parallel or

series.

Filtration Rate 3.0-6.0 gpm/ft2

Depending upon mode of operation.

Maximum Feed Flowrate 25 gpm

Filter Diameter 24 inches 6-inch flanges top and bottom.

Filter Height 72 inches

Filter Construction FRP FRP shell, polyethylene liner.

Underdrain - - - - Gravel-less type with IMS Cap

Filter Media Configuration

Filter 1: Mono-media

Anthracite

Depth 40 inches

Effective Size 1.0 mm

Filter 1A: Tri-mediaAnthracite

Depth 20 inches


Sand

Depth 8 inches


Sand

Depth 6 inches


Filter 2: Dual-media

Anthracite

Depth 20 inches

Effective Size 1.0 mmSand

Depth 10 inches


Air Scour 13 SCFM 4 SCFM//ft2

(if required)

Backwash Flowrate 48 gpm

P Backwash Interval 5-15 psi With option of timed interval


37/254


A B-4

Table B-4

Slow Sand Filter Equipment Design CriteriaItem Quantity Unit Description/Notes

Flow 8-12 gpmFiltration Rate 0.08-0.12 gpm/ft2

Filter Tanks 2 No. HDLPE

Volume (each) 1,500 gallons

Dimensions

Diameter 8 feet

Height 8 feet

Filter Bed Layers

Filter 1: Fine Media

Bottom 10 inches Graded gravel

Top 24 inches Sand (effective size =0.35 mm)

Filter 2: Coarse Media

Bottom 10 inches Graded gravel

Top 24 inches Sand (effective size =0.80 mm)

Table B-5

Pressurized UF Equipment Procurement Design Criteria


Norit Unit

Feed Flow 8-15 gpm

Membrane Material PES

Membrane Area 377 or 753 sq ft Depending on number of modules

Recovery Rate 90-95 %

Flux Rate 20-60 gfd

Nominal Pore Size 0.01 micron

CIP Chemicals Required

Citric Acid 1 No. Feed systemSodium Hypochlorite 1 No. Feed system

Table B-6

Immersed UF Equipment Procurement Design CriteriaItem Quantity Unit Description/Notes

Zenon Zeeweed 1000

Feed Flow 8-15 gpm

Membrane Material PVDF

Membrane Area 600-1,800 sq. ft. Depending upon no. of modules

Recovery Rate 90-95 %

Flux Rate 12-36 gfd Depending upon no. of modules

Nominal Pore Size 0.02 micronCIP Chemicals Required

Citric Acid 1 No. Feed system

Sodium Hypochlorite 1 No. Feed system


38/254

TM2: RO Configuration Investigation


39/254

A TM2-1

TM2: RO Configuration InvestigationIntroduction

This technical memorandum (TM) summarizes the results from Investigation 2 of the scwd2seawater reverse

osmosis (SWRO) desalination pilot-scale study: an evaluation of reverse osmosis membranes and

configurations.

The desalinated water quality data collected and analyzed during the pilot program is summarized in TM No.

11, Treated Water Quality Goals and Results.

This TM focuses on the salts (and associated regulations) which will determine the selection of the RO

membranes and process configuration. These salts include sodium, chloride, bromide, and boron. See TM No. 3

for the evaluation of operational strategies to further reduce boron concentrations in the desalinated water.

Summary and Conclusions

1. As shown in Figures A-5 through A-9 in Appendix A, the single-stage low energy SWRO configuration

membrane combination achieves:

The proposed chloride goal of 150 mg/L for taste and irrigation.

The DPH boron regulation & the proposed boron goal for irrigation of 1 mg/L.

The proposed bromide goal of 0.5 mg/L to reduce TTHM formation.

2. Adding a 25% partial 2nd pass with boron specific LPRO membranes:

Reduces boron by an additional 15-30% (increases w/ pH adjustment).

Reduces bromide by an additional 45%. Based on the results shown in Figure 11, it is anticipated that up

to a 40% reduction in bromide (to 0.3 mg/L) may be necessary at times to minimize impacts on TTHM

formation.

Allows for membranes with lower energy use to be installed in the first pass.

Additionally, a partial 2nd pass will provide a safety factor in case the salt rejection of the RO membranes

decreases more quickly than expected due to frequent cleanings or unforeseen circumstances. It will

likely be cheaper to operate a partial second pass on an as-needed basis than to replace most or all of

the RO membranes sooner than expected.


40/254

City of Santa Cruz & Soquel Creek Water District TM2: RO Configuration Investigation

TM2-2 A

3. The two-stage LPRO/SWRO configuration:

Reduces energy use at recovery rates greater than 55% compared to single-stage SWRO and two-stage

SWRO/SWRO configurations.

Does not achieve the chloride, boron or bromide goals during long-term use.

Becomes a more viable option for a source with lower salt concentrations including beach wells.

4. Increasing RO system flux reduces salt concentrations (e.g., an increase from 8 gfd to 9 gfd decreases boron

and bromide concentrations by approximately 10%). However, this may increase the fouling rate

depending on source water quality and the type of pretreatment.

Recommendations

CDM recommends that the seawater desalination plant use one of the following RO configuration and

membrane alternatives:

1. Low energy SWRO membranes in a single-stage configuration followed by a 25% partial second pass.

2. High rejection SWRO membranes in a single-stage configuration.

3. Combining low energy and high rejection SWRO membranes in a single-stage configuration.

Each of these alternatives would produce a RO permeate that meets the key water quality objectives of 1.0

mg/L of boron, 0.5 mg/L of bromide, 150 mg/L of chloride, and 80 mg/L of sodium during summer months

when the highest source water temperatures are expected. These water quality objectives are important when

considering boron regulations, irrigation water quality objectives, customer satisfaction and DBP regulations.

The above recommendation on RO configuration and membrane alternatives assumes that: (1) there are notsignificant changes to the current operation of GHWTP with respect to DBP precursor removal and DBP

formation, and (2) it is not cost-effective to build a pipeline so that treated Graham Hill WTP water is blended

with the RO permeate before it is discharged to the distribution system. The pipeline was originally considered

to provide water for blending to reduce pipeline corrosion. However, it was determined not provide a benefit

in terms of DBP reduction as long as the first assumption does not change.

CDM will have further discussions with the Water Department and District about these assumptions prior to the

July 20/21 workshop. CDM also will analyze costs and non-cost factors for each RO membrane alternative prior

to the July 20/21 workshop.

Testing Goals and ObjectivesThe objectives were to:

1. Evaluate the energy use of the three RO configurations tested.


41/254

TM2: RO Configuration Investigation City of Santa Cruz & Soquel Creek Water District

A TM2-3

2. Assess the salt rejection of the RO membranes and system configurations in terms of achieving water

quality regulations and goals for irrigation. See Appendix B for information on typical sodium, chloride and

boron limits for irrigation.

3. Test innovative 2-stage RO configuration to reduce the energy requirement at the proposed facility.

Background

The RO membranes selected for the study were membranes recommended by the four pre-selected

manufacturers (Hydranautics, Toray, Dow Filmtec, and Saehan) to provide the lowest energy use, while also

achieving water quality regulations (the selection was driven primarily by the DPH notification goal for boron of

1 mg/L). Hydranautics, Toray, and Dow Filmtec are the three manufacturers typically specified for municipal

scale projects in the U.S. Saehan is relatively new to the U.S. market, but may provide significant cost savings if

membrane performance and warranty conditions are satisfactory. Additional testing of a Saehan product is

recommended prior to procurement due to the limited amount of installations for drinking water and concerns

observed during pilot-testing at other locations in California (e.g., West Basin and Camarillo).

The following three configurations were tested to assess impacts on energy use and water quality:

Figure 1 provides a schematic of the standard single-stage SWRO configuration. This configuration was

tested as the baseline for comparison because it is typically the option with the lowest energy use and RO

system equipment costs.

Figure 2 provides a schematic of the single-stage RO configuration followed by a partial second pass. This

configuration was tested to confirm performance in achieving boron concentrations of less than 1.0

milligrams per liter (mg/L).


42/254


TM2-4 A

Figure 3 provides a schematic of the two-stage LPRO/SWRO configuration, which utilizes LPRO membranes

in the first stage instead of SWRO membranes. This configuration was tested to assess the potential energy

savings of utilizing LPRO membranes in the first stage which require less pressure and therefore energy use.

The two-stage LPRO/SWRO configuration was tested because initial projections indicated that it could

reduce energy use at recovery rates of 55% or greater when compared to single-stage SWRO and 2-stageSWRO/SWRO configurations. Figure 4 displays the results of these initial projections; a reduction of 1.0 kWh

per 1,000 gallons provides a reduction in power costs of approximately $100,000 per year assuming 2.5 mgd

of RO permeate and a unit cost of $0.13 per kWh. The reduction in energy use is due to the lower pressure

requirements of LPRO membranes; the tradeoffs are that the LPRO membranes reject fewer salts and that a

second high pressure booster pump is required between the first and second stage. The second stage

utilizes SWRO membranes with higher salt rejection to treat the remaining seawater. The design includes

combining the RO permeate streams from each stage to improve water quality.

Note energy recovery devices were not used due to the size of the pilot systems. ERDs are typically utilized for

larger systems.

A two-stage SWRO/BWRO configuration has been used at full-scale desalination plants in other countries to

increase overall recovery rate of the plant . Increasing the recovery rate reduces the amount of source water

required, which reduces the size of the intake and pretreatment equipment. The disadvantage of the two-stage

SWRO/SWRO configuration is that it requires higher system pressures, which increases energy use and

operation and maintenance requirements. This indicates that the two-stage configuration will also be more

expensive to operate. Additionally, it will require a higher construction cost than a single stage system due to

the increased number of pressure vessels and pumps and will be more complex to startup and shutdown than

a single stage system due to the increased number of pumps, automated valves, and pressure balancing

requirements.


43/254


A TM2-5

Key Operating and Water Quality Parameters

RO Equipment Design CriteriaThe RO systems were designed to operate given the following parameters:

2 skids, each with 2 independent RO trains

Number of RO membrane elements per train: up to 8

Membrane element: 4 inch diameter, 40 inches long

Flux rate per train: 8 to 10 gfd

Recovery: 40 to 55%

Figures A-1 and A-2 in Appendix A provide an illustration of the impact of flux and recovery rate on energy use

and salt rejection based on RO design software calculations.

Source Water QualityThere are three source water quality periods in Monterey Bay which will impact the performance of the RO

process. These are the summer months, fall and spring months, and winter months. The key water quality

Figure 4Projected Energy Use Prior to Pilot Testing


44/254


TM2-6 A

parameters for these periods are summarized in Table 1. See Figures A-3 and A-4 for an illustration of

temperature on overall salt rejection and pH of boron rejection.

Table 1. Daily Average Source Water Quality Summary(1)

Water Quality Parameter Units Fall & Spring Winter Summer

Temperature oC 12 to 14 10 to 13 13 to 16

pH pH Units 8.0 7.9 8.0

Total Dissolved Solids mg/L 36,000

Chloride mg/L 20,000

Sodium mg/L 11,000

Boron mg/L 4.5

Bromide mg/L 70(1)

Data from samples collected at the pilot plant and proposed open ocean intake.

The variation in source water quality conditions can be summarized as follows:

Source water boron, total dissolved solids (TDS) and pH remain relatively constant year-round.

Average daily temperatures ranged from approximately 10 degrees Celsius (oC) in the winter months to

16oC during the summer months. A 0.5 to 1.0oC increase in temperature was observed at the pilot plant

between the seawater intake and the RO system. This is also expected at the full-scale plant.

RO feedwater pH was reduced by 0.2 to 0.5 pH units at the pilot plant when ferric chloride was added at

doses of 5 to 25 mg/L to improve the pretreatment process.

Relevant Drinking Water Quality RegulationsThe following regulations will be relevant to the selection of the RO membranes and configurations:

Secondary maximum contaminant levels (MCLs) for salty taste: TDS 500 mg/L and chloride 250 mg/L.

California Department of Public Health (DPH) Notification level for boron: 1 mg/L or 1.44 mg/L after

rounding.

Primary MCLs for disinfection by-products: total trihalomethanes (TTHM):


45/254


A TM2-7

Table 2. Average Salt and Boron Rejection for Different RO Membranes and RO System Configurations

RO System Configuration RO Membrane Membrane

Description

Salt Rejection(1)(%)

Boron Rejection

(%)

Single Stage

Hydranautics SWC5(1)Low energy

product99.5% 76-82%

Toray 810L(1)Low energy

product99.2-99.5% 72-78%

Saehan RELow energy

product99.5% 80%

Dow Filmtec SW30 XLELow energy

product99.4% 76%

Single Stage followed by a

partial 2nd RO pass

1st pass: Toray 810L

2nd pass: Hydranautics ESPAB

Boron specific

LPRO membrane>99.7% 86%

Two-stage LPRO/SWRO1st stage: Hydranautics ESPAB

2nd stage: Toray 810L

Boron specific

LPRO membrane99.0% 65%

(1)Salt and boron rejection can vary depending on temperature, pH and system recovery

(2)Note that multiple sets of Hydranautics SWC5 and Toray 810L membranes were tested at the pilot plant because two sets of

the Hydranautics membranes were initially tested downstream of the Norit and GMF pretreatment systems from April to August2008..One set of Toray membranes was tested downstream of the Zenon pretreatment system from April to August 2008; newToray membranes were installed downstream of all pretreatment systems from August 2008 and operated until April 2009.

During pilot plant operations, salt and boron rejection improved with the addition of the partial second pass

downstream of the single-stage configuration. The salt and boron rejection were significantly lower for the

two-stage configuration as expected.

ESPAB membranes were selected as the LPRO membrane for both configurations because the membrane

material has been developed for enhanced boron rejection. This improvement was confirmed when compared

to ESPA2 membranes, which are considered standard LPRO membranes for brackish water applications.

Figure 5 compares the TDS concentration observed during testing versus the concentration projected by RO

design software. The chart shows that the observed salt rejection was similar to the projected salt rejection,

with the exception of the Toray 810L and the 2-stage configuration. Note that several sets of Toray 810L

membranes were installed and only one set performed as well as expected.

The results indicate that the single-stage and 2nd pass configurations will perform as expected, but the two-

stage configuration may exhibit lower salt rejection than expected. Assuming the standard 10% decrease in salt

rejection per year, the two-stage configuration will not achieve the secondary MCL for chloride of 250 mg/L

after 5 years of operation even when utilizing higher rejection membranes in the second stage.


46/254


TM2-8 A

Figure 6 compares the boron concentration observed during testing with the concentration projected by RO

design software. Note that the boron concentration in the source water ranged from 3.7 to 5.2 mg/L (themajority of samples were between 4.3 and 4.5 mg/L) with some variability depending on the method used for

analysis1 and dilution from runoff during storm events.

The results indicate that the boron concentrations were under-predicted by RO design software (up to 8%) for

all of the configurations. Assuming a 10% decrease in salt rejection per year, the single-stage configuration will

not achieve the DPH notification level for boron of 1.4 mg/L depending on water temperature after the two

years of operation using the low energy membranes. However, this goal will be achieved with the single-

stage configuration by (1) using membranes with higher salt rejection or (2) adding a partial second pass

downstream.

1 EPA methods 200.7 and 200.8 were used for measuring boron concentration depending on the suite of secondary in

organics and metals selected for analysis.

Figure 5Comparison of Observed and Projected TDS Concentrations

0

50

100

150

200

250

300

350

400

450

500

Singlestage

w/SWC5

Singlestage

w/810L

Singlestage

w/SW30XLE

Singlestage

w/RE

Singlestagew/

810L&20%2nd

Passw/ESPAB

2Stage

LPRO/SWROw/

ESPAB&810L

RangeofTDSResuls(mg/L)

ObservedResults ProjectedResults


47/254


A TM2-9

The two-stage system did not achieve the DPH notification level for boron of less than 1.4 mg/L. According to

projections, utilizing high rejection SWRO membranes with enhanced boron rejection in the second stage (e.g.,

Hydranautics SWC4+B instead of Toray 810L) will improve boron rejection. However, this configuration would

still not achieve the DPH notification level for boron or the secondary MCL of 250 mg/L for chloride at all times

during long-term use.

Figure 6Comparison of Observed and Projected Boron Concentrations

0.00

0.20

0.40

0.60

0.80

1.00

1.20

1.40

1.60

1.80

2.00

Singlestage

w/SWC5

Singlestage

w/810L

Singlestage

w/SW30XLE

Singlestage

w/RE

Singlestagew/

810L&20%2nd

Passw/ESPAB

2Stage

LPRO/SWRO

w/ESPAB&810L

RangeofBoronResuls

(mg/L)

Observed Results Projected Results


48/254


TM2-10 A

Figure 7 compares TDS rejection to the rejection of bromide, sodium and chloride at the pilot plant. As

expected, TDS rejection is consistent with the rejection of mono-valent ions.

The results confirm that the rejection of TDS correlates with the rejection of sodium, chloride, and bromide,

which is not always included in RO design software projections.

Figure 8 compares the energy use for the three different configurations during pilot testing. The energy use

was calculated by placing a power meter on the electrical power connection to the high pressure RO feed

pump and VFD only and did not include additional power requirements of controls or instrumentation because

these additional loads would be a much lower percentage of power use for a full-scale system. SWROmembranes were low energy membranes; LPRO membranes were high boron rejection products.

98.0%

98.2%

98.4%

98.6%

98.8%

99.0%

99.2%

99.4%

99.6%

99.8%

100.0%

03/21/08 05/08/08 06/25/08 08/12/08 09/29/08 11/16/08 01/03/09 02/20/09

PercentageRemova

lofTDSandMonovalentIons(%)

Date

TDS Sodium Chloride Bromide

Figure 7Comparison of TDS Rejection and Bromide,

Chloride and Sodium Rejection


49/254


A TM2-11

The results indicate that all configurations will perform as expected in terms of energy use without energy

recovery. The two-stage LPRO/SWRO configuration required approximately the same amount of energy at 55%recovery as the single-stage required at 45%.

However, as previously noted, the two-stage configuration will not achieve regulatory limits for boron or

chloride during long-term operation when used an open intake source. If a subsurface intake with lower salt

concentrations is constructed for the full-scale plant, the two-stage configuration would be a more viable

option.

Hydranautics, Toray, and Dow Filmtec are the three manufacturers typically specified for municipal scale

projects in the U.S. Although the 4 Toray SWRO membranes did not perform as well as expected in terms of

salt rejection, 8-inch Toray membranes have performed as expected at the Moss Landing pilot study and at full-

scale facilities in the U.S. and around the globe. The Saehan membranes performed as expected in terms ofwater quality, but required a significantly higher operating pressure than the other membranes tested. Thus, it

is not recommended that Saehan membranes be included in design specifications unless better results can be

demonstrated at other facilities such as testing planned at the Affordable Desalination Coalition pilot facility or

other Saehan SWRO facilities.

Figure 8Comparison of Pilot Plant Power Use Results for the

Three RO System Configurations

0.0

2.0

4.0

6.0

8.0

10.0

12.0

14.0

16.0

18.0

SinglestageSWRO

Flux:8gfd

Recovery:45%

SinglestageSWRO

Flux:10gfd

Recovery:50%

20%LPRO2ndPass

Flux:14gfd

Recovery:85%

TwostageLPRO/SWRO

Flux:8gfd

Recovery:55%

InitialEnergyUsewithoutEnergyRecovery(

kWh/kgal)


50/254


TM2-12 A

The pilot plant results in Santa Cruz and experiences at other pilot-scale and full-scale facilities demonstrate

that RO design software is adequate for predicting salt rejection (e.g., TDS and mono-valent ions), but may

under-predict boron rejection. This is important to understand as RO design software will be used by RO

system designers, membrane manufacturers and equipment suppliers to estimate costs and to comply with

performance-based specifications for the full-scale facility.

Projected Long-term Energy Use and Water QualityEnergy use increases and salt rejection decreases as RO membranes age. This is due to multiple variables

including but not limited to membrane compaction, degradation, fouling, and cleaning frequency. The

following charts are based on RO design software projections and assume the following:

Average membrane replacement frequency of 5 years. Parameters presented in this TM at a 5-year

membrane age are thus expected to be representative of parameters (e.g., energy use and water quality

concentrations) during long-term use because membranes are expected to be replaced every five years on

average.

7% flux decline and 10% salt rejection decline per year.

RO feedwater quality as follows:

Temperature: 10 to 17oC

pH of 7.6 after coagulation; boron concentrations would likely be 10% lower on average at a pH of 8.0

when operating without a coagulant

TDS concentration of 36,000 mg/L

Chloride concentration of 20,000 mg/L

Bromide concentration of 70 mg/L

Boron concentration of 4.5 mg/L

Low energy (LE) SWRO membranes are defined as membranes that would provide a RO system with an

initial salt rejection of 99.5% at 8 gallons per foot per day (gfd) and 45% recovery.

High Rejection (HR) SWRO membranes are defined as membranes that would provide a RO system with

an initial salt rejection of 99.7% at 8 gfd and 45% recovery.

Low pressure (LP) RO refers to the low pressure RO membrane products typically used for brackish water

sources.

RO design software provided by Hydranautics, Toray and Dow Filmtec was used for the projections.

Figure 9 shows the projected power use at 5 years for each configuration with energy recovery at 14oC.

Projections were sent to two energy recovery device manufacturers (Energy Recovery International and Pump

Engineering, Inc.) to estimate the amount of power that could be recovered from the RO concentrate stream

prior to discharge. The projected power use with energy recovery is compared to the power use without


51/254


A TM2-13

energy recovery during pilot testing to provide an indication of how much energy can be recovered for each

configuration.

The projections indicate that (1) the single-stage configuration will have the lowest energy use after energy

recovery, (2) a 25% partial second pass adds a minor increase in energy use, and (3) less energy is available for

recovery when using the two-stage configuration. When considering the actual energy (i.e., with energyrecovery), the 0.7 kWh per 1,000 gallons savings provided by the single-stage configuration vs. 2-stage

configuration is worth approximately $85,000 per year assuming 2.5 mgd of RO permeate and a unit power

cost of $0.13 per kWh.

Figure 10 compares boron concentrations during expected summer water quality conditions (17oC and pH =

7.5) during long-term use (5 year RO membrane age) based on projections using RO design software. The

projected concentrations in Figure 10 were increased by 8% based on pilot plant testing results which

indicated that projection software may under-predict boron rejection by as much as 8%.

Figure 9Comparison of Projected Initial Energy Use For Each RO Membrane

Configuration Before and After Energy Recovery

15.4

16.3

14.8

9.710.5 10.4

0

3

6

9

12

15

18

Single Stage(45% recovery)

Single Stage +aPartial 2nd Pass(45% Recovery)

2-stage LPRO/SWRO(55% recovery)

Power(kWh/1,0

00gallonsl)

w/o Energy Recovery

w/ Energy Recovery


52/254


TM2-14 A

The projections indicate that: (1) the single-stage configuration can achieve a boron concentration that is lower

than the DPH notification goal during long-term use; (2) the single-stage followed by a 25% partial second pass

can achieve a boron goal significantly less than 1.0 mg/L during long-term use; and (3) the two-stage

LPRO/SWRO configuration will not achieve the DPH notification goal during long-term use even if recently

developed high boron rejection LPRO and SWRO membranes are selected.

Figure 11 compares the relationship between the concentration of bromide in the RO permeate and TTHM

formation after blending with treated surface water in the distribution system. TM No. 7 includes additional

information on the DBP formation testing and results during pilot testing.

Historically, bench-scale tests have overestimated TTHM formation from the Graham Hill water treatment plant.

After reviewing this data in the context of historical DBP data in the system, the results indicate that bromide

concentrations greater than 0.5 mg/L may significantly increase TTHM formation after blending with treated

surface water within the distribution system. The increase is due to chlorination converting bromide to

bromine, which reacts with TTHM precursors in the treated surface water to create brominated TTHMs.

Figure 10Projected Long-term Boron

Concentrations During Summer Months

1.21

0.99

0.83

1.55

0.0

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

SingleStageSWRO

with"LE"Membranes

SingleStageSWRO

with"LE"&"HR"

Membrane

Combination

SingleStage&a

25%2ndROPass

2stage

LPRO/SWRO

Boron(mg/L)

DPHNotificationLevel

Proposedgoalforirrigation


53/254


A TM2-15

Brominated TTHM concentrations measure approximately double the concentrations of chlorinated TTHMs

because the molecular weight of bromide is double the molecular weight of chloride, which is a component of

chlorinated TTHMs. In conclusion, the testing showed that it is important to set a bromide goal in the

desalinated water to the impacts on TTHM formation in the system.

Figure 12 compares the expected bromide concentrations at 17oC during long-term use (5 year RO membrane

age) based on projections using RO design software.

0

20

40

60

80

100

120

140

Test1:bromide=0.5mg/L Test2:bromide=0.8mg/L Test3:bromide=0.3mg/L

TTHMs5daysafterchlorination(ug/L)

100%GrahamHillWater 25%Blend 50%Blend 100%DesalinatedWater

MCL=80ug/L

Figure 11Total Trihalomethanes Formed In 0%, 25%, 50%, and 100% RO Permeate

Blends at Different RO Permeate Bromide Concentrations

TTHMs5daysafte

rchlorination(g/L)


54/254


TM2-16 A

The projections indicate that: (1) the single-stage SWRO configuration will at a minimum require a combination

of low energy and high rejection membranes to achieve a bromide goal of 0.5 mg/L; (2) the single-stage

SWRO with LE membranes followed by a 25% partial second pass can achieve a bromide goal of less than 0.3

mg/L; and (3) the two-stage LPRO/SWRO configuration using high rejection LPRO and SWRO membranes will

not achieve a bromide goal of 0.5 mg/L.

0.6 0.5

0.3

1.1

0.0

0.3

0.5

0.8

1.0

1.3

1.5

SingleStageSWRO

with"LE"Membranes

SingleStageSWRO

with"LE"&"HR"MembraneCombination

Single Stage&a

25%2ndROPass

2stage

LPRO/SWRO

Bromide(mg/L)

ProposedgoaltominimizeTTHMformation

Figure 12Expected Long-term Bromide

Concentrations During Summer Months


55/254

Appendix ARO Projection

Data Charts


56/254

FigureA1.ImpactofRecoveryand

Fluxo

nPowerRequirements

Membraneflux=

8g

fd

Membraneflux=

9g

fd

Membraneflux=

10g

fd

OptimalPerformanceRan

ge

12

.0

12

.5.

11

.0

11

.5

0gallons)

9.5

10

.0

10

.5

Use(kWhr/1,0

8.5

9.0

Power

8.0

35%

40%

45%

50%

55%

60%

%Recovery

Note

:DataprojectedbyRODesignSof

tware

usingwaterqualitycollectedduringpilottesting.


57/254

FigureA2.ImpactofRecoveryand

FluxonSaltRejection

Mem

brane

flux=

8g

fd

Mem

brane

flux=

9g

fd

Mem

brane

flux=

10gfd

99

.9%

.

99

.7%

99

.8%

)

99

.5%

99

.6%

altRejection(

99

.4%

99

.3%

35%

40%

45%

50%

55%

60%

%Recovery

Note:DataprojectedbyRODesignSoftware

using

waterqualitycollectedduringpilottesting.


58/254

FigureA3.ImpactofTemperature

onSaltRejection

Power

(assumes

45%

Recovery

&8g

fdflu

x)

Sa

ltRe

jec

tion

(assumes

45%

recoveryan

d8g

fdflux

)

99

.66%

99

.68%

99

.70%

11.6

11.8.

99

.62%

99

.64%

11.2

11.4

)

00gallons)

99

.56%

99

.58%

99

.60%

10.6

10.8

11.0

altRejection(

Use(kWhr/1,0

99

.52%

99

.54%

10.2

10.4

S

Power

99

.50%

10.0

10

.0

11

.0

12

.0

13

.0

14

.0

15

.0

16

.0

17

.0

Temperature(Celcius)

Note:

DataprojectedbyRODesignSoftw

are

using

waterqualitycollectedduringpilo

ttesting.


59/254

1.2

1.4

1.6

1.8

2.0

)

FigureA4.ProjectedBoron

Concent

rationsafter

pHAdjustment

99

.5%

SRMem

branea

tFee

dwa

terpH

=7

.6

99

.5%

SRMem

branea

tFee

dwa

terpH

=8

.0

99

.5%

SRMem

branea

tFee

dwa

terpH

=8

.5

CADPHEffectiveNotificationLevelAfterRou

nding

0.0

0.2

0.4

0.6

0.8

1.0

0

1

2

3

4

5

Boron(mg/L

YearsofOperation

Note1:

DataprojectedbyRODesignSoftwareusingwater

qualitycollectedduringpilottesting.

Note2:

Concentrationsat5yearsrepresenttheexpected

longter

mconcentrationrange.


60/254

1.2

1.4

1.6

1.8

2.0

)

FigureA5.ProjectedBoron

ConcentrationsForDifferentRO

Membranes

(SinglestageConfiguration)

99

.3%SaltRejectionMembrane

99


99


99


CADPHEf

fectiveNotificationLevelAfterRou

nding

0.0

0.2

0.4

0.6

0.8

1.0

0

1

2

3

4

5

Boron(mg/L

YearsofOperation

Note1:DataprojectedbyRODesignSoftwareusing

waterqualitycollectedduringpilottesting.

Note2:Concentrationsat5yearsreprese

nttheexpected

long

termconcentrationrange.


61/254

FigureA

6.Projecte

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